JP2005223446A - Filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter capable of maintaining low insertion loss characteristics of a stored filter with a very simple structure in which the inner wall of a casing is composed of a superconductor. <P>SOLUTION: A coplanar filter is provided with a dielectric substrate 1, a plurality of resonators 5a, 5b, 5c, and 5d which are composed of a center conductor 2 formed on the same surface of the dielectric substrate 1 and ground conductors 3a, 3b formed in parallel on both sides of the center conductor 2, and input/output terminal parts 4a, 4b. The inner wall of the casing 10 of the coplanar filter is composed of the superconductor 100. The casing 10 of the coplanar filter is composed by sticking a superconductor film-forming substrate, in which the film of a high-temperature superconductor such as a lanthanum system, an yttrium system, a bismuth system, and a thallium system is formed on a substrate made of an metal oxide material such as MgO, SrTiO<SB>3</SB>, LaGaO<SB>3</SB>, and LaAlO<SB>3</SB>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a filter, and more particularly to a filter used for transmitting and receiving signals in mobile communication, satellite communication, fixed microwave communication, and other communication technology fields.

In recent years, a filter using a conductor as a superconductor has been proposed as a filter applied to transmission / reception of microwave communication, and the filter structure is also a cavity resonator type structure, a microstrip line structure, or a planar circuit of a coplanar line structure. Various types of structures are used, including molds.
The concept of the coplanar line will be described with reference to FIG. In FIG. 10, 1 is a dielectric substrate, 2 is a central conductor, 3a is a first ground conductor, and 3b is a second ground conductor. The central conductor 2, the first ground conductor 3a, and the second ground conductor 3b are formed on the common surface of the dielectric substrate 1 in a parallel and coplanar state, and when forming an inductive coupling portion, a via hole is formed. There is a great degree of freedom in design, starting with things that are not necessary.

A conventional example of a filter using a coplanar line will be described with reference to FIG. 1 (see Non-Patent Document 1). The coplanar filter includes a center conductor 2 having an electrical length corresponding to a quarter wavelength on the dielectric substrate 1, and first ground conductors 3a formed on both sides of the center conductor 2 with a spacing s. a second ground 3b, a first capacitive coupling portion 6a composed of a gap g ₁ provided at the center conductor 2 of the center conductor 2 and the first resonator 5a of the first input-output terminal portion 4a, the second a second capacitive coupling portion 6b which is composed of the resonators 5b central conductor 2 and the third resonator 5c gap g ₂ formed between the center conductor 2 of a central conductor 2 of the fourth resonator 5d No. a third capacitive coupling portion 6c which is composed of two gaps g ₃ formed between the center conductor 2 of the input and output terminal portion 4b, provided at the junction of the first resonator 5a and second resonator 5b The center conductor 2 is electrically connected between the first ground conductor 3a and the second ground conductor 3b. The first inductive coupling portion 8a configured by the tangential line conductor 7a, the central conductor 2, the first ground conductor 3a, and the second ground conductor 3b provided at the junction of the third resonator 5c and the fourth resonator 5d. And a second inductive coupling portion 8b configured by a short-circuit line conductor 7b that electrically connects the two. Note that the characteristic impedance of the coplanar line is determined by the center conductor width w of the center conductor 2 shown in FIG. 10 and the ground conductor interval d (w + 2s) between the first ground conductor 3a and the second ground conductor 3b. Is done.

Further, the dielectric substrate 1 of FIG. 1 is accommodated in a metal casing 10 shown in FIG. 11, and has a configuration in which electromagnetic wave energy radiated from the coplanar filter is recovered again by this filter.
H. Suzuki, Z. Ma, Y. Kobayashi, K. Satoh, S. Narahashi and T. Nojima, "a low-loss GHz bandpass filter using HTS quarter-wavelength coplanar waveguide resonators," IEICE Trans. Electoron., Vol. E-85-c, No.3, pp.714-719, March 2002.

In the above conventional example, the electromagnetic wave energy radiated from the filter accommodated in the metal casing 10 is almost reflected by the inner surface of the metal casing 10, and most of the radiated electromagnetic energy is recovered by the filter. A part of the current flows as an induced current in the metal inside the metal housing 10, resulting in a radiation loss. In particular, in the filter in which the characteristic impedance of the resonators 5a to 5d is larger than the characteristic impedance of the input / output terminal portions 4a and 4b, there is a problem that the loss further increases because the ratio of the radiated electromagnetic wave energy is large.
An object of the present invention is to provide a filter that maintains a low insertion loss characteristic of a housed filter with a very simple structure in which the inner wall of the casing is made of a superconductor.

Claim 1: It has a plurality of resonators 5a to 5d and input / output terminal portions 4a and 4b constituted by the dielectric substrate 1, the central conductor 2 and the ground conductor 3 formed on the surface of the dielectric substrate 1, In the filter having the housing 10 including the dielectric substrate 1, a filter in which the inner wall of the housing 10 is composed of the superconductor 100 was configured.
A second aspect of the present invention includes a dielectric substrate 1, and a plurality of center conductors 2 formed on the same surface of the dielectric substrate 1 and ground conductors 3a and 3b formed in parallel on both sides thereof. In the coplanar filter including the resonators 5a, 5b, 5c, and 5d and the input / output terminal portions 4a and 4b, a coplanar filter in which the inner wall of the housing 10 is formed of the superconductor 100 is configured.

Further, in the filter according to any one of claims 1 and 2, the housing 10 is made of a lanthanum-based metal oxide material substrate such as MgO, SrTiO ₃ , LaGaO ₃ , or LaAlO _3. A filter comprising a superconductor film-forming substrate on which high-temperature superconductors such as yttrium-based, bismuth-based, and thallium-based films were attached to the inner wall was constructed.
Further, in the filter according to any one of claims 1 to 3, the characteristic impedance of the resonators 5a, 5b, 5c, and 5d is set to be higher than the characteristic impedance of the input / output terminal portions 4a and 4b. Configured a large filter.

Here, in the filter described in claim 5: claim 4, the characteristic impedance is:
Z ₀ = (η ₀ / 4√ε _eff ) × (K ′ (k) / K (k))
Where ε _eff is the effective dielectric constant of the coplanar line,
η ₀ is the free space wave impedance,
K (k) is a complete elliptic integral of the first kind,
'Is the derivative,
Furthermore, ε _eff = 1 + ((ε _r −1) / 2) × (K ′ (k) / K (k))
× (K (k ₁ ) / K ′ (k ₁ ))
η ₀ = √ (μ ₀ / ε ₀ ) = 120π
K (k) = ∫ ₀ ¹ dx / {(√ (1-x ² )} × (1-k ² x ² ))
k = w / d
k ₁ = sinh (πw / 4h) / sinh (πd / 4h)
The characteristic impedance Z ₀ is determined by the ratio k of the center conductor width w to the ground conductor interval d, the dielectric constant ε _{r of} the dielectric substrate, and the dielectric substrate thickness h, and the center conductor width with respect to the ground conductor interval d A filter with a characteristic impedance Z ₀ increased was constructed using the ratio k of w as a parameter.

  According to the present invention, the low insertion loss characteristic of the accommodated filter is maintained by accommodating the filter using the conductor as the superconductor in the housing having a very simple structure in which the inner wall is composed of the superconductor. A filter can be provided. Further, by using a low power loss casing whose inner wall is made of a superconductor, it is possible to realize a reduction in loss of the filter and duplexer. Further, by using these low insertion loss filters and duplexers, it is possible to achieve low insertion loss and low noise in the high frequency transmission / reception unit of the communication device.

An embodiment of a coplanar filter in which the circuit board of the coplanar filter shown in FIG. 1 is housed in a metal casing shown in FIG. 2 having an inner wall made of a superconductor will be described.
A center conductor 2 having an electrical length corresponding to a quarter wavelength on the dielectric substrate 1, and a first ground conductor 3a and a second ground conductor 3b formed on both sides of the center conductor 2 with a spacing s between them. When, the center conductor 2 and the first capacitive coupling portion 6a composed of a gap g ₁ provided at the center conductor 2 of the first resonator 5a of the first input-output terminal portion 4a, the center of the second resonator 5b a second capacitive coupling portion 6b made of a conductor 2 and the third resonator 5c gap g ₂ formed between the center conductor 2 of the center conductor 2 and the second output terminal of the fourth resonator 5d a third capacitive coupling portion 6c constituted by 4b gap g ₃ formed between the center conductor 2 of a central conductor 2 provided at the junction of the first resonator 5a and second resonator 5b first Consists of a short-circuit line conductor 7a that electrically connects the first ground conductor 3a and the second ground conductor 3b. The first inductive coupling portion 8a is electrically connected to the center conductor 2 provided at the junction of the third resonator 5c and the fourth resonator 5d with the first ground conductor 3a and the second ground conductor 3b. And an inductive coupling portion 8b constituted by a short-circuit line conductor 7b.

As described above, when the filter is housed in the metal casing, there is power W consumed as radiation loss in addition to the current flowing through the conductor, and the current I induced on the inner wall of the metal casing and the inner wall of the metal casing From the surface resistance R, W = RI ² is obtained. However, as shown in FIG. 2, by configuring the inner wall of the casing using the superconductor, the power W consumed in the casing can be reduced, and the insertion loss of the filter can be reduced. As will be described later, it is particularly effective for a filter in which the characteristic impedance of the resonator is larger than the characteristic impedance of the input / output terminal section.

In general, the relational expression between current and voltage on the distributed constant line is
I _i, V _i: a current value of the traveling wave, the voltage value I _i, V _i: a current value of the reflected wave, the voltage value gamma: propagation constant alpha: attenuation constant beta: phase constant
Z: Characteristic impedance
R: Series resistance
L: Series inductance
G: Parallel conductance C: Expressed by capacitance, the current value on the distributed constant line is inversely proportional to the characteristic impedance.

Here, the coplanar type line will be described. The characteristic impedance of the coplanar line is
Z ₀ = (η ₀ / 4√ε _eff ) × (K ′ (k) / K (k))
It is expressed. Here, ε _eff is the effective relative permittivity of the coplanar line, η ₀ is the free space wave impedance, K (k) is the first type complete elliptic integral, and 'represents the differentiation. Furthermore,
ε _eff = 1 + ((ε _r −1) / 2) × (K ′ (k) / K (k)) × (K (k ₁ ) / K ′ (k ₁ ))
η ₀ = √ (μ ₀ / ε ₀ ) = 120π
K (k) = ∫ ₀ ¹ dx / {(√ (1-x ² )} × (1-k ² x ² ))
k = w / d
k ₁ = sinh (πw / 4h) / sinh (πd / 4h)
The characteristic impedance Z ₀ is determined by the ratio k of the center conductor width w to the ground conductor interval d, the dielectric constant ε _{r of} the dielectric substrate, and the dielectric substrate thickness h. Therefore, as shown in FIG. 3, the characteristic impedance Z ₀ can be increased using the ratio k of the center conductor width w to the ground conductor interval d as a parameter.

  In consideration of the above, another embodiment of the present invention will be described with reference to FIG. FIG. 4 shows an embodiment in which a resonator having a characteristic impedance of 100Ω is combined with an input / output terminal portion 4 having a characteristic impedance of 50Ω, for example. That is, in FIG. 4, the input / output terminal portion 4a and the first resonator 5a, the second resonator 5b and the third resonator 5c, and the fourth resonator and the input / output terminal portion 4b are coupled by capacitive coupling. This is an embodiment of a quarter-wavelength four-stage coplanar filter constructed by inductive coupling between the first resonator 5a and the second resonator 5b, and between the third resonator 5c and the fourth resonator 5d. . The characteristic impedance of the first input / output terminal portion 4a and the second input / output terminal portion 4b was set to 50Ω from the viewpoint of matching with the characteristic impedance of the device connected to these input / output terminal portions. In this case, an MgO substrate having a dielectric constant of 9.68 is used as the dielectric substrate 1, the central conductor width w of the first input / output terminal portion 4a and the second input / output terminal portion 4b is 218 μm, and the ground conductor interval d is 400 μm. . The center conductor width of the first resonator 5a to the fourth resonator 5d is 218 μm, the ground conductor interval d is 1,780 μm, and the characteristic impedance of these resonators is 100Ω.

The current density distribution of the embodiment of the above-described quarter wavelength four-stage coplanar filter is shown in FIG. 5 and FIG. 6 showing an enlarged part thereof. In any of the first resonator 5a to the fourth resonator 5d, the current density distribution is a node of the first capacitive coupling unit 6a, the second capacitive coupling unit 6b, and the third capacitive coupling unit 6c, and the first induction. The sexual coupling portion 8a and the second inductive coupling portion 8b are substantially sinusoidal, and this point is the same as the current density distribution of the conventional coplanar filter shown in FIGS. However, since the characteristic impedances of the first resonator 5a to the fourth resonator 5d are designed and manufactured to be large, the current density in each resonator is reduced, and the maximum current density is also the conventional example shown in FIGS. About 45%, and about 70% reduction in terms of electric power.
Further, in this embodiment, when the central conductor 2 and the first and second ground conductors are formed of, for example, a lanthanum-based, yttrium-based, bismuth-based, thallium-based or other high-temperature superconductor, Since the current density could be reduced, there is less risk of current exceeding the critical current of high-temperature superconductors, and the low-loss effect of the superconducting coplanar filter is sufficiently achieved without destroying the superconducting coplanar filter. Can be demonstrated.

By the way, although the filter in which the characteristic impedance of the resonator is larger than the characteristic impedance of the input / output terminal portion can reduce the current density, the radiation loss is particularly increased. The power W consumed in the case as radiation loss is obtained as W = RI ² from the current I induced in the conductor and the surface resistance R of the conductor. In the embodiment shown in FIG. 4, assuming an example in which a case of a copper plate with gold deposited at a height of 4.5 mm from the dielectric substrate 1 is installed in the metal case 10 of FIG. Is 0.0063 db. On the other hand, as shown in FIG. 2, the loss can be further reduced by housing the filter in a casing having an inner wall made of a superconductor. An example of the insertion loss reduction in this case is shown in FIG. In this example, the in-band insertion loss is reduced by about 0.001 db.

In FIG. 2, as a method of applying the superconductor 100 to the inner wall of the housing 10, for example, a lanthanum-based, yttrium-based, bismuth-based, thallium-based or other high-temperature superconductor is formed by sputtering, vacuum evaporation, CVD. A method of attaching a superconductor film-forming substrate formed on a metal oxide material substrate such as MgO, SrTiO ₃ , LaGaO ₃ , or LaAlO _{3 to} the inner wall of the casing by a method, a thick film method, or other film forming methods. Convenient. Further, as the characteristic impedance is increased, the effect of reducing the loss of the inner wall of the housing is greater.
The above description of the description is an explanation of an example of a coplanar filter configured based on a coplanar transmission line. By the way, as a transmission line on which the filter configuration is based, a transmission can be configured by appropriately designing and adjusting both the characteristic impedance of the input / output terminal portion and the characteristic impedance of the resonator formed in the transmission line. As long as it is a line, a transmission line having any structure other than a coplanar line such as a grounded coplanar line or a microstrip line can be used as well.

The figure explaining a coplanar filter. The figure which shows the coplanar filter accommodated in the metal housing | casing which applied the superconductor to the inner surface. The figure which shows the characteristic impedance with respect to the ground conductor space | interval center conductor width ratio. The figure explaining an Example. FIG. 5 is a current density distribution diagram of the embodiment of FIG. 4. The figure which expanded and showed a part of current density distribution of FIG. The current density distribution figure of a prior art example. The figure which expanded and showed a part of current density distribution of FIG. The figure which shows the comparison of the reduction effect of insertion loss. The figure explaining the concept of a coplanar track | line. The figure which shows the coplanar filter accommodated in the metal housing | casing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dielectric board | substrate 2 Center conductor 3a 1st ground conductor 3b 2nd ground conductor 4a 1st input / output terminal part 4b 2nd input / output terminal part 5a 1st resonator 5b 2nd resonator 5c 3rd resonator 5d 4th resonance 6a 1st capacitive coupling part 6b 2nd capacitive coupling part 6c 3rd capacitive coupling part 7a Short circuit conductor 7b Short circuit conductor 8a 1st inductive coupling part 8b 2nd inductive coupling part 9 Edge line 10 Metal enclosure Body 100 Superconductor d Ground conductor spacing g ₁ , g ₂ , g ₃ gap s Spacing between the center conductor and the first ground conductor, the second ground conductor w Center conductor width

Claims (5)

In a filter having a plurality of resonators constituted by a dielectric substrate and a central conductor and a ground conductor formed on the surface of the dielectric substrate and an input / output terminal portion, and having a casing including the dielectric substrate,
A filter characterized in that the inner wall of the housing is made of a superconductor. A coplanar comprising a dielectric substrate, and comprising a plurality of resonators and input / output terminal portions composed of a central conductor formed on the same surface of the dielectric substrate and ground conductors formed in parallel on both sides thereof In the filter,
A coplanar filter characterized in that the inner wall of the housing is made of a superconductor. In the filter according to any one of claims 1 and 2,
The casing is a superconductor film-forming substrate in which a high-temperature superconductor such as lanthanum, yttrium, bismuth, or thallium is formed on a metal oxide substrate such as MgO, SrTiO ₃ , LaGaO ₃ , or LaAlO _3. A filter characterized by comprising a material attached to an inner wall. In the filter according to any one of claims 1 to 3,
A filter characterized in that the characteristic impedance of the resonator is larger than the characteristic impedance of the input / output terminal portion. The filter according to claim 4, wherein
Characteristic impedance is
Z ₀ = (η ₀ / 4√ε _eff ) × (K ′ (k) / K (k)),
Where ε _eff is the effective dielectric constant of the coplanar line,
η ₀ is the free space wave impedance,
K (k) is a complete elliptic integral of the first kind,
'Is the derivative,
Furthermore, ε _eff = 1 + ((ε _r −1) / 2) × (K ′ (k) / K (k))
× (K (k ₁ ) / K ′ (k ₁ ))
η ₀ = √ (μ ₀ / ε ₀ ) = 120π
K (k) = ∫ ₀ ¹ dx / {(√ (1-x ² )} × (1-k ² x ² ))
k = w / d
k ₁ = sinh (πw / 4h) / sinh (πd / 4h)
The characteristic impedance Z ₀ is determined by the ratio k of the center conductor width w to the ground conductor interval d, the dielectric constant ε _{r of} the dielectric substrate, and the dielectric substrate thickness h, and the center conductor width with respect to the ground conductor interval d The characteristic impedance Z ₀ was increased using the ratio k of w as a parameter.
A filter characterized by that.